In the context of this invention, the term enclosure refers to a structure, inside which can be established a sealed space. The enclosure comprises at least a front wall, a rear wall, as well as panel type walls defining a depth of the enclosure. The enclosure is also capable of being split along a division plane or boundary surface at least for a base section and a lid section, which are disengageably fastenable to each other. Typically, the enclosure is used for protecting electrical, pneumatic, optical or the like connections or equipment from external influences, such as physical contact, effects of ambient air, moisture, dust, UV radiation, etc. A few examples of the enclosure include, among others, distribution boxes, distribution cabinets, pneumatics cabinets and the like. A joint between the base section and the lid section can be effected for example by means of threaded connecting elements such as screws or by means of hinges and a clasp.
Electric cables and the like to be extended into enclosures, such as distribution boxes and the like, must be capable of being delivered through a wall of the enclosure. Depending on the installation site of an enclosure, various properties are required in the enclosure as regards tightness of the enclosure. These various conditions and a tightness class consistent therewith are determined in standard SFS-EN 60529 whereby, in the event that an enclosure fulfils certain qualifications set forth in the standard, the enclosure has a tightness which is for example IP 55 or IP 65. One objective for an enclosure lead-through and a grommet, making up the object of this invention, is to provide a solution matching the class IP55 or IP 65 of the cited standard.
The connections present inside the enclosure may not be subjected by way of a cable to pulling, pushing, bending, twisting or other such force. Hence, the actual connection point must be in a mechanically strainless condition, which is why the enclosures are provided at a lead-through point with a so-called strain relief mechanism. A strain possibly existing in a cable outside an enclosure is transmitted by this strain relief mechanism to the enclosure structure, the segment of cable thus ending up inside the enclosure in a strainless condition.
The prior art discloses various solutions for such an application which functionally requires both sealing and strain relief in an enclosure lead-through.
One traditional solution is a socket sealing to be threaded on a cable and tightened with a nut. For such a device, the wall of an enclosure is typically drilled to form a hole, followed by placing outside the enclosure a socket-like element which is mounted on the enclosure wall either by a retaining nut or by a screw thread present in the socket-like element. The socket-like element has generally further in connection therewith a seal or seals as well as sealing faces for ensuring a proper tightness between the socket, the cable and the enclosure. The cable is threaded through both and the joint is tightened. The result of this is a very tight and solid construction, which nevertheless requires a linear thread-through cable plain without prefitted connectors or the like. One example of applying such a solution is described in the publication U.S. Pat. No. 5,676,339, although the application in this case is not actually a screw-threaded but quick release-fastened lead-through socket.
Another traditional solution is a lead-through mechanism to be threaded on a cable and placed in a U- or V-shaped recess, which opens from a division plane between the lid and base sections of an enclosure, said mechanism comprising a rubber-like lead-through collar, which seals between the recess and the lid and features a hole matching the cable diameter, and which is split either partially or all the way. Such split rubber seals provide a useful solution, but a sufficient sealing effect and strain relief are difficult to achieve because of inconsistent cable diameters and symmetry defects involved therein.
One solution is a lead-through mechanism to be threaded on a cable and placed in a U- or V-shaped recess, which opens from a division plane between the lid and base sections of an enclosure, wherein a traditional sealing socket can be set tightly in a recess without threading it through a hole in the enclosure wall. In this solution, the lead-through mechanism is installable in separate operations first on a cable and only then on a wall of the enclosure, but the socket and the nut still require a plain threadable linear cable without prefitted connectors or the like.
One solution is also a collar type split version, “stocks”, which is applicable with several cable to be led through. The strain relief features and the sealing features of this solution do not match those of the above-described solutions. If a high-quality sealing is desired in such “stocks” designs, its achievement requires a construction with a high compression force. Thus, the structure shall most often be expensive, complicated, and inconvenient to install.
Another publication known from the prior art is JP 2002142344, disclosing a lead-through liner or rather a water stop plug to be mounted on the end of a cable protective tube. Here, the liner is split for two parts, said half-liners aligning themselves relative to each other by means of corrugated guide faces. The external surface is sealed to the cable protective tube by means of a long urethane material attached with the help of a double-faced tape.
The prior art discloses also the publication JP 08251769, wherein the water tightness of a two-component lead-through seal has been improved by forming the division surface with complementary grooves and lands as well as with guide faces for an improved, alignment.
Another publication known from the prior art is U.S. Pat. No. 4,993,724, wherein a conduit seal is hingedly splitable and the conduit seal can be fit tightly around a conduit by using bolts to tighten the axially seal-penetrating flanges present on either side of an elastic seal element.